Electrical sensing strips are widely used on door edges to provide safe power door operation. A person or object in the door closure path causes the strip to deform and an electrical contact to close, resulting in immediate deenergization or reversal of the drive motor. Thus injury to the person or object obstructing closure of the door is prevented.
One type of sensing strip, disclosed in U.S. Pat. No. 3,315,050 to Miller, utilizes a pair of foam pads carrying conductive aluminum sheets. Intermediate the foam pads is another foam strip formed with openings. Upon deformation of the outer foam pad, the aluminum sheets are forced into contact through one of the openings to close a suitable circuit.
Operating problems occur with the Miller type strips when the strip jacket is ruptured by abrasion or puncture, permitting moisture and contaminants to enter the foam pads. This causes the foam between the aluminum contacts to become conductive, resulting in short circuits between the aluminum sheets. Door closure is interrupted, a serious disadvantage in power door operation.